The art of drawing blood from patients for testing purposes has in recent years centered around the use of blood drawing devices that utilize pre-evacuated containers or tubes in which the blood tests are actually carried out. These devices normally include a dual needle assembly which includes a hypodermic needle and a tap needle which is used for tapping the evacuated container. To facilitate the taking of multiple samples, such devices also include a holder for the evacuated containers. In use the holder is coupled to the needle assembly and serves as a holder for the container during the blood drawing process as well as a structure for guiding the tap needle and container stopper into a vacuum tapping relation at which the needle has penetrated the stopper and is in communication with the sterile contents of the vessel.
Certain problems are encountered in using pre-evacuated containers. For one, the blood withdrawals are sometimes so rapid as to cause collapse of the patient's vein. This is undesirable because the need then arises to seek out another vein to collect the blood specimen and with all the well known patient trauma that is associated with the use of hypodermic needles. Yet another problem which is encountered is that of mechanical hemolysis caused by a shearing action on blood cells that transpires with rapid movement of the blood through the assembly components. Such hemolysis results in unsatisfactory specimens that must be discarded and again secured from the patient.
The vein collapsing problems can be generally overcome by providing a suitable valve mechanism between the hypodermic needle and the evacuated container. This permits the hospital technician or other attendant to regulate the flow of blood under the action of the partial vacuum in the sterile container to a rate which avoids collapsing of the patient's vein. This flow regulation also tends to minimize mechanical hemolysis but a further avoidance of the problem results from the use of streamlined flow structures in the mounts for and at the proximal ends of the needles.
Various different types of valve arrangements have been advocated and used in the dual needle assemblies. Many have involved the use of complicated structures which are too expensive to utilize in disposable items. Others have parts that can be accidentally disassembled during use of the devices. This, of course, requires the technician to start over again with a new sterile assembly and under circumstances which frequently follow an initial penetration of patient tissue by the hypodermic needle. Yet other valve arrangement require the use of both hands in order to manipulate the valve, and under circumstances where it would be preferable to have one hand free to perform other tasks.
The need accordingly exists for an inexpensive needle assembly of the kind contemplated in which the parts are reliably coupled together and protected from disassembly during use and in which the blood flow can be easily and effectively regulated by the technician.
A general object of the invention is to provide improvements in blood drawing devices. One particular object is to provide improvements in dual needle assemblies that are used with evacuated containers in blood drawing devices. Still another object is to provide a needle assembly of the kind contemplated and wherein the blood flow may be regulated by the attendant by a simple means for constricting the passage through a resilient tube. Other objects of the invention are to provide a simple, inexpensive means for regulating the flow of blood between the needles of a dual needle assembly and which during the process of manufacturing the disposable item, can be readily assembled by the workers. Other objects will be evident hereinafter.